In various plants, each of which is provided with a boiler, a steam generator and the like and uses high-temperature water, including a thermal power plant and a nuclear power plant, there may cause a case where a metal of a structural material is subjected to an aged deterioration phenomenon such as ionic elution and the formation of a corrosion product. Deposition of the corrosion product disturbs a flow channel in a pipe, resulting in a cause of vibration.
Furthermore, the vibration under a high flow-velocity condition may cause a crack or damage in the structural material, and in addition, when the corrosion product deposits on a heat transfer surface in the steam generator of a pressurized-water nuclear power plant, a feed water heater or the like of a boiling-water reactor power plant or a thermal power plant, the corrosion product may cause the decrease of the heat transfer coefficient.
In such steam generator and feed water heater, an impurity concentration in feed water is kept at low concentration by continuous blow water in the apparatus, but in a narrow portion such as a crevice portion between a heat transfer pipe and a support plate, water quality occasionally differs from a controlled value, which may result in that the impurities are concentrated in the narrow portion, a corrosive environment is created in the portion, and it may also be assumed that a scale (oxide) or the like deposits therein. In addition, even in the piping in a pipeline having an orifice, a valve or the like, a liquid passes through the inner space at a high speed, and accordingly, in such case, it is necessary to take measures against erosion, corrosion, flow-accelerated-type corrosion and the like.
These are representative phenomena occurring in high-temperature water environment, and exert various influences such as a problem on an operation caused by corrosion and increase of maintenance frequency on the piping and other members including the structural material. In addition, in recent years, such a phenomenon occurs in a carbon steel pipe that the thickness of the pipe decreases due to a wall-thinning phenomenon. Thus, the elution, the corrosion phenomenon and the like of metal are gradually accumulated during a plant operation in a long period of time, and potentially show a possibility of suddenly erupting into a disaster at some point.
In any power plant, in a pipeline on a downstream side of a condenser, iron and the like elute, and in a pipe disposed downstream side of a deaerator, the temperature rises and a condition of causing the flow-accelerated-type corrosion is formed. Because of this reason, the suppression of these phenomena leads to the enhancement of the soundness and the operation period of equipment. The method of suppressing the above descried phenomenon includes injecting a chemical agent having a corrosion-suppressing effect into the system to impart a quality of causing little corrosion to the water, for example, in the thermal power plant, the PWR power plant and the like.
For example, in a secondary system of the thermal power plant or the pressurized-water-type nuclear power plant, pH control or water quality control has been performed by injecting ammonia for reducing the elution of iron from the inside of the system and preventing the inflow of the iron to the steam generator. Furthermore, in order to eliminate the alkali concentration of the crevice portion in the steam generator, various water quality controls are implemented in an actual plant, such as an Na/Cl ratio control and a chloride ion concentration control for reducing an influence of a chlorine ion on corrosion. In recent years, the water-quality control method has been adopted by using improved chemicals such as ethanolamine and morpholine.
As for the improvement of chemicals to be injected, there is provided a method of utilizing an organic acid such as tannic acid and ascorbic acid as an oxygen scavenger (for example, as disclosed in Japanese Patent Laid-Open Publication No. 4-26784: Patent Document 1). In addition, as for the water-quality control method, there are proposed an operation method of controlling a molar ratio of all cations/SO4, a method of introducing at least one of a calcium compound and a magnesium compound into feed water to a steam generator for a nuclear reactor so that the ion concentration becomes 0.4 to 0.8 ppb (for example, as disclosed in Japanese Patent Laid-Open Publication No. 2004-12162: Patent Document 2), and the like. In addition, a technology for injecting a precious metal for protecting a material and injecting oxygen is also proposed (for example, as disclosed in Japanese Patent Laid-Open Publication No. 10-339793: Patent Document 3).
However, the methods of controlling the water quality proposed in the Patent Documents 1 and 2 inject the chemical agent into the feed water of the pressurized-water-type nuclear power plant, and accordingly, this technology may apply an influence upon the purity of the feed water, the environment and the like.
Furthermore, although the method of controlling the water quality disclosed in the Patent Document 3 shows clear criteria for the injection of the precious metal such as platinum (Pt) and ruthenium (Ru), there is no disclosure concerning a necessary injection amount and an injection method for a metal compound such as titanium oxide (TiO2).